Monday, March 26, 2007

Why the Greeks could hear plays from the back row
The wonderful acoustics for which the ancient Greek theatre of Epidaurus is renowned may come from exploiting complex acoustic physics, new research shows.

The theatre, discovered under a layer of earth on the Peloponnese peninsula in 1881 and excavated, has the classic semicircular shape of a Greek amphitheatre, with 34 rows of stone seats (to which the Romans added a further 21).

Its acoustics are extraordinary: a performer standing on the open-air stage can be heard in the back rows almost 60 metres away. Architects and archaeologists have long speculated about what makes the sound transmit so well.

Now Nico Declercq and Cindy Dekeyser of the Georgia Institute of Technology in Atlanta say that the key is the arrangement of the stepped rows of seats. They calculate that this structure is perfectly shaped to act as an acoustic filter, suppressing low-frequency sound — the major component of background noise — while passing on the high frequencies of performers' voices1.

The apparent fly in the ointment is stated within the article: Declercq cautions that the presence of a seated audience would alter the effect, however, in ways that are hard to gauge. "For human beings the calculations would be very difficult because the human body is not homogeneous and has a very complicated shape," he says. That is, when people are seated, the seats are largely covered up by soft, squishy people wearing soft, squishy clothing. OTOH, it might still be designed for the ideal and still work reasonably well even when the reflective surfaces are partly covered.